Synchronously gated active night sight

ABSTRACT

A night sight employing a gated image intensifier is operated in conjunction with an amplitude-modulated tracking beacon on a missile and a pulsed light source for illuminating the target. The source is pulsed and the intensifier tube gated on for the target return magnet attached illumination such times that the amplitude modulated beacon intensity is at a low level for minimium viewing interference.

United States Patent [1 1 Maxwell, Jr. et al.

SYNCHRONOUSLY GATED ACTIVE NIGHT SIGHT [451 Sept. 25, 1575 3,219,82611/1965 Letaw, Jr. 244/3.16 3,478,212 11/1969 Turck r 250/203 R3,467,773 9/1969 Heckman, .lr.... 178/68 2,930,894 3/1960 Bozeman244/3.13

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-S. C. Buczinski[22] Filed; Sept, 22, 1972 Attorney-llarry M. Saragovitz et al. [21]Appl. No.: 291,511

[57] ABSTRACT 52 us. C1 356/152, 178/DIG. 21, 356/5, A night Sightemploying a gated image intensifier is p- 244/313 2444316 erated inconjunction with an amplitude-modulated 51 lnt. c1. Gtllc 3/03 treekihgheeeeh on a missile and a pulsed light some [58] Field of Search 250/203R; for illuminating the target The seuree is Pulsed and the 7 131 2 35 45 152; 24 43 3 intensifier tube gated on for the target return magnetattached illumination such times that the amplitude 5 References Citedmodulated beacon intensity is at a low level for UNITED STATES PATENTSminimium viewing interference.

3,640,628 2/1972 Jones 244/3. 16 41 Claims, 3 Drawing Figures 1 22 23 IPULSED PRF I2 ILLUIVIINATOR GENERATOR 1 1 1 TARGET I a 1 GATED RANGENIGHT TIME SlGHT DELAY I 1 L i BEACON I I BEACON CROSSING f 7 MODULATIONDETECTOR a I I3 DETECTOR TIME DELAY PAIENIED E Z 3,781.1 80

' sum 2 OF 2 BEACON RADIANT INTENS'TY ILLUMINATOR PULSE REFLECTED TARGETI PULSE /IMAGE TUBE 4--RANGE DELAY GATE PULSE BACKGROUND OF THEINVENTION A class of guided missiles has been developed for tactical usewhich employs a command-to-line-of-sight mechanization. A sight line toa target is established with an optical sight. After launch toward thetarget, the missile is guided by means of an optical error sensingdevice which measures the error or deviation of the missile from thedesired line of sight and furnishes command signals to the missilecontrol system by means of an encoder and data link; thereby causing themissile to follow the line of sight to the target.

In order to provide a tracking source for the optical tracker, a beaconis placed on the missile. This beacon usually comprises anamplitude-modulated source of optical radiation. The modulation providesa signature which permits the tracker to discriminate againstunmodulated sources such as sunlight reflections from random objects inthe tracker field of view.

The optical spectrum of the beacon may be such that it can be seen bythe eye. In daylight conditions the use of an optical filter would besatisfactory in reducing the beacon brightness to a tolerable levelwithout inhibiting the ability of the gunner to maintain his line ofsight on the target.

However, ifa night sight is to be used with such a missile system, thedegree of optical filtering necessary to reduce the beacon intensity toa tolerable level may also reduce the overall light level to a valuewhich would seriously inhibit the trackers ability to see the target.The instant invention solves this problem.

SUMMARY OF THE INVENTION Since the beacon is amplitude-modulated, theradiant intensity varies with time from a very low value (essentiallyzero) to a peak value during each cycle.

If a night sight, which employs a gated image intensitier tube is used,the tube can be gated on for very short periods of time such that it ison at the time that the beacon radiant intensity is at its lowest value.The gating of the night sight is, therefore, so synchronized with thebeacon modulation that the beacon irradiance at the night sight is keptat a tolerable value.

Since the gating of the image intensifier results in a reduction in thetime during which the target is observed, the average radiant intensityfrom the target and scene is reduced. In order to provide the necessarytarget radiant intensity a pulsed illumination source is employed. Thesource is pulsed to illuminate the target and the image intensifiergating is timed so that the sight is gated on at the time that theradiant energy of the illuminated target returns to the night sight.

In order to provide a synchronizing signal to the illuminator and gatedimage intensifier tube, an optical radiant intensity sensor is employed.This sensor responds to the beacon modulation and provides means forsensing the time at which the beacon intensity is at its lowest value,thereby providing the necessary information for the synchronization ofilluminator and gating.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows the optical tracking andguidance of a I FIG. 3 depicts the time-history relationship of thebeacon modulation, illuminator pulse and the image intensifier tubegating pulse.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I, a visual sight Idproviding a line of sight is associated with an optical tracker II.Visually sighting to target I2 aligns the boresight axis of the opticaltracker with this target. The optical tracker receivesamplitude-modulated radiant pulses from a beacon I3 on missile II. Theoptical tracker I I having error sensing means therein measures theerror or deviation of the missile from the desired line of sight. Acommand encoder I5 receives error signals from the tracker II andprovides command signals to a command transmitter Id which sends thecorrective signals to the missile Ml thereby causing it to follow thedesired line of sight to the target.

Turning to Figure 2, we see, diagrammatically, the sight III of theinstant invention and the associated beacon suppression components. Thesight M, which is a synchronized active night sight, can be described asfollows. The beacon modulation waveform is sensed by a beacon modulationdetector 20. The detected signals are sent to a crossing detector andtime delay in element 2I. Electronic circuits comprising the crossingdetector in element 2I detect the time at which the beacon radiantintensity has decreased to percent of its peak value. A time delay ofone-quarter of the modulation period is used to generate a synchronizingpulse. This synchronizing pulse triggers a pulsed illuminator 22 by wayof a PRF generator 23 when the beacon radiant intensity is near itlowest level. The pulsed illuminator could, for example, comprise anarrow spectral bandwidth source such as gallium arsenide or galliumaluminum arsenide. The illuminator optical pulse is transmitted to thetarget I2 and reflected therefrom to the night sight 25. A range timedelay 24!- operating in response to a signal from the PRF generator 23provides a signal to the gated night sight 25 to gate the imageintensifier tube on just as the optical pulse returns from the target.By these means, the target is observed when the beacon radiant intensityis at its lowest value resulting in minimum viewing interference by thebeacon I3.

Additional beacon suppression is provided by a narrow optical bandpassfilter 2b which passes the pulsed illuminator energy but not the radiantenergy of the beacon.

The time-history of FIG. 3 shows the illuminator pulse generated afterthe one-quarter modulation period delay, and the image tube gate pulsebeing generated at the time of the returning reflected target pulse.

The device of the instant invention could, for example, incorporate asecond generation image intensifier tube employing a singlephotoemissive photocathode, a microchannel plate amplifier and a singlephosphor screen; such tube providing speed of response and peak pulsecapabilities compatible with the overall system requirements of thisdevice.

While a preferred embodiment of the invention has been disclosed, itshould be clear that variations and alterations thereof can be madewhile remaining within the scope of the invention which is only limitedby the following claims.

We claim:

1. An optical command-to-line-of-sightguidance system having an activenight sight for use with a missile having an amplitude-modulated beaconof optical radiation thereon, said system comprising:

when the beacon amplitude is at a low level and the pulsed illuminationreflected from said target has returned to said night sight.

2. The system of claim 1 wherein said electronic cirphotoresponsivemeans for detecting the radiant en- 5 cuit means includes further meansfor establishing a ergy amplitude of the missile beacon;

electronic circuit means including means for determining the time atwhich the beacon amplitude has decreased to a pre-determined level fromits peak amplitude and for generating a synchronizing signal thereat;

means for generating an illumination pulse along the line of sighttoward a missile target in response to said synchronizing signal;

a gated night sight capable of being gated on in response to an appliedsignal;

range time delay means responsive to a signal derived from saidsynchronizing signal to gate on the gated night sight; whereby the nightsight is gated on time delay in said synchronizing signal; said timedelay being on the order of one-quarter of the beacon modulation period.

3. The system of claim 2, further including a pulse repetition frequencygenerator for receiving said synchronizing signal and utilizing saidsynchronizing signal for triggering the illumination pulse, saidgenerator further activiating said range time delay for gating on saidnight sight;

said generator further activating said range time delay for gating onsaid night sight.

4. The system of claim 3 including a narrow bandpass filter associatedwith said gated night sight.

. UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No.3,761,180 Dated 25 September 1973 Inventor-(S) Richard F. Maxwell, Jr.and Jose E. Tallet It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

On the front page, between data. elements and 22] insert -83] Assignee:The United States of America as represented by the Secretary of theArmy".

Signed and sealed this 19th day of March 1974.

(SEAL Attestz' v I EDWARD 'M.FLETCH ER, JR. c. MARSHALL DA'NN AttestingOfficer Commissioner of Patents *ORM Po-1osq (10-69) USCOMM-DC 60376-P69t 0.5. GOVERNMENT pamrmc OFFICE I969 o-aas-au UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,761,180 Dated 25 September1973 Inventor(s) Richard F. Maxwell, Jr. and Jose E. Tallet It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

on the front page, between data elements [75] and 22] insert -[73]Assignee: The United States of America as represented by the Secretaryof the Army-n Signed and sealed this 19th day of March 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,'JR. c. MARSHALL DA'NN Attesting Officer Commissionerof Patents ORM PQAOSQ (10-69) USCOMM-DC 60376-P69 u.s. GOVERNMENT rnmnucornc: I969 o-ass-Ju

1. An optical command-to-line-of-sight guidance system having an active night sight for use with a missile having an amplitudemodulated beacon of optical radiation thereon, said system comprising: photoresponsive means for detecting the radiant energy amplitude of the missile beacon; electronic circuit means including means for determining the time at which the beacon amplitude has decreased to a prEdetermined level from its peak amplitude and for generating a synchronizing signal thereat; means for generating an illumination pulse along the line of sight toward a missile target in response to said synchronizing signal; a gated night sight capable of being gated on in response to an applied signal; range time delay means responsive to a signal derived from said synchronizing signal to gate on the gated night sight; whereby the night sight is gated on when the beacon amplitude is at a low level and the pulsed illumination reflected from said target has returned to said night sight.
 2. The system of claim 1 wherein said electronic circuit means includes further means for establishing a time delay in said synchronizing signal; said time delay being on the order of one-quarter of the beacon modulation period.
 3. The system of claim 2, further including a pulse repetition frequency generator for receiving said synchronizing signal and utilizing said synchronizing signal for triggering the illumination pulse, said generator further activiating said range time delay for gating on said night sight; said generator further activating said range time delay for gating on said night sight.
 4. The system of claim 3 including a narrow bandpass filter associated with said gated night sight. 